'What's new in video is audio': the vibrant sound and many voices of tomorrow's television

This fall, watchers of KTLA-TV, an independent station in Los Angeles, will be able to tune into reruns of ''Love Boat'' and ''Little House on the Prairie'' in either English or Spanish. They may also catch the local nightly news in their choice of two languages - and pick up movies and special events (like the January Rose Parade) in full stereo.

KTLA will be among the first stations in the United States moving into a long-awaited type of broadcasting - ''multichannel sound TV'' - that will allow stereo telecasts as well as other novel features, such as bilingual broadcasting.

Stereo TV, as it's called, is expected to be one of the biggest changes to hit the industry since color. But its penetration of the airwaves will be gradual. Its arrival in the United States is also belated. Europe has had it on a limited basis for almost two years and Japan since 1978.

The go-ahead for the move into stereo came in March with approval by the Federal Communications Commission (FCC). TV stations are now allowed to use three audio channels. Two of them will be for beaming stereo signals.

The third can be used in a variety of ways: for broadcasting programs in a second language; carrying descriptions for the blind; offering two levels of narration in education or sports programs - the Japanese, for instance, sometimes give viewers the choice of two announcers for baseball games, one sympathetic to the home team and the other partisan to the challengers.

Upgrading TV's sound is one more attempt at satisfying a growing consumer clamor for better audio in general. In cars, FM stereo has become as popular as smile-face key chains. There is now a push on for AM stereo. Television - perhaps the last holdout in improving sound - has been undergoing some changes as well. For the past three years, manufacturers have been putting stereo speakers in their top-quality sets. These can create pseudo-stereo sound by splitting the signal into high and low frequencies.

Full-fledged stereo has been available to these set owners through videocassette movies and other programs prerecorded in stereo. ''Hi-fi'' sound, too, has been carried through the telecast of musical series in conjunction with local FM radio stations. Viewers watch the picture on their screens but listen to their radios. MTV, the cable service, has used this technique to telecast music videos as well.

What the new system would do is put stereo signals directly over the airwaves , eliminating the necessity to link up with a radio station or rely solely on prerecorded video material.

TV-makers are agog over the prospect. It may revive sales of high-priced models. ''What's new in video is audio,'' says Frank McCann of RCA Corporation's consumer electronics division.

But don't expect your TV to resonate with stereophonic sound very quickly. For one thing, sets have to be equipped to receive the signals. This includes internal electronics as well as the right speakers. A few manufacturers are just now beginning to produce high-end models with built-in decoders and amplifiers. But these aren't expected to be on store shelves in any numbers until late next year (at $100 to $150 above the normal cost). ''Black box'' converters, meanwhile, are being developed for most existing models. These will allow consumers either to pick up the stereo sound through their own sets or pipe it through their hi-fis. Prices are expected to vary from $50 to $200.

Another snag is that TV networks and local stations also have to retool to transmit the signals - a costly process for something that won't necessarily guarantee bigger audiences. The major networks are only cautiously moving toward stereo. The first few programs will be carried this fall. ABC, for instance, plans to test a stereo transmission at one station in Los Angeles later this year. NBC will beam several programs in 1985, including the ''Tonight Show'' and ''Friday Night Videos.'' CBS has been more reticent - partly because some 95 percent of its program schedule is ''dialogue oriented'' and won't draw audiophiles. But some network executives also argue that there is no need to jump until they know how high consumer demand and available stereo programming will be.

Programs targeted for such broadcasting, of course, will be those where sound is prominent: video music shows, movies, and some entertainment and sports programs. Tests of stereo broadcasts have indicated that the difference from conventional TV can be dramatic. With some sporting events, for example, it gives the feeling of ''being there.'' Even in dramatic presentations, actors' stage positions can be suggested by the audio ambiance. Yet there are limits to the number of sound-rich shows. ''Stereo sound is not imperative to watch 'The $ 25,000 Pyramid,' '' says David Fischer, an analyst with Arthur D. Little Inc., the consulting firm.

What might spur a quicker move into stereo broadcasting by networks and stations is the third audio channel, particularly its potential for bilingual broadcasting. Offering bilingual versions of hit shows and news programs - particularly to Hispanics - could lure more viewers. ''This is what stations have their eyes on,'' says David Lachenbruch, editorial director of Television Digest, an industry newsletter. ''In some markets it could mean one rating point - that's gold.'' Yet there are snags here, too: What Spanish dialect do you broadcast?

Ultimately, some observers predict, everything will eventually be telecast in stereo. But the transition, like that to color, will be gradual. ''We may be looking at a very good saturation in five years,'' says Ralph Haller, chief engineer of the FCC's mass-media bureau.